Blade edge structure for core drill

ABSTRACT

A cutting portion structure of a core drill having diamond grains may affect deformation of a tip end portion of a cutting blade after extended use. A core drill A comprises cutting blades  2  formed at an opening end portion  4  of a cylindrical core body  1  and arranged in a circumferential direction of the core body to have gaps  3  between the cutting blades  2 . As viewed from a direction substantially perpendicular to a cross-sectional view in a radial direction of the core body  1 , the opening end portion  4  has an end face  4 A which is rounded without edges, and diamond grains are bound on the opening end portion  4  which is rounded without edges from an inner peripheral side to an outer peripheral side, thereby forming the cutting blades  2.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of priority of InternationalPatent Application Ser. No. PCT/JP03/16211 filed on Dec. 18, 2003, whichapplication claims priority of Japanese Patent Application Ser. No.2002-369433 filed Dec. 20, 2002. The entire text of the priorityapplication is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention generally relates to a core drill which issuitable for use in drilling holes with a relatively large diameter.More particularly, the present invention relates to a cutting portionstructure of a core drill which is suitable for use in drilling holeswith a large diameter in concrete, stone, etc.

BACKGROUND ART

Traditionally, in order to carry out drilling holes smoothly, acombination of a cylindrical core body provided with drilling cuttingblades at a peripheral edge portion of an opening and a center drillprovided at a center of the core body has been used as a core drill foruse in drilling holes with a large diameter.

In such a core drill, first, the center drill drills a center hole, andthereafter, the core body rotates around the center drill positioned inthe center hole to drill a large diameter hole which is a target holearound the center hole.

An exemplary construction for the cutting portion structure of the coredrill of this type which is for use in drilling holes in concrete,stone, etc, is such that cutting blade chips which are made of cementedcarbide or bound with diamond grains are embedded in concave portionsformed in an opening end of the core body with appropriate gaps betweenthem and attached thereto by brazing or the like (Japanese Patent No.252057).

However, the core drill constructed such that the cutting blade chipsincluding the diamond grains are attached on the periphery of theopening end of the core body is by far more expensive than other coredrills, since expensive diamond grains are used in portions which areaccommodated in the concave portions and do not perform cutting.

It is possible that the diamond grains are bound in a layered structureon an outer peripheral face, an inner peripheral face, and an end faceof the opening end portion of the cylindrical core body. In that case,if such a core drill is used in drilling holes in concrete, stone, etc,the diamond grains in a region on which stress concentrate on tend towear out and disengage from the core body in a relatively short time. Asa result, the life of the core drill greatly decreases.

The present invention has been made under the circumstances, and anobject of the present invention is to provide a cutting portionstructure of a core drill which is capable of efficiently utilizingexpensive diamond grains without wear or disengagement after a long-timeuse, and of thereby maintaining high cutting ability (drilling ability)for a long time period.

DISCLOSURE OF THE INVENTION

In order to achieve the above described object, a cutting portionstructure of a core drill including a cylindrical core body; and cuttingblades, comprises an opening end portion formed on the cylindrical corebody, the opening end portion being rounded as viewed from a directionsubstantially perpendicular to a cross-section in a radial direction ofthe core body, wherein the cutting blades are formed at the opening endportion of the cylindrical core body and arranged in a circumferentialdirection of the core body to have gaps between the cutting blades, andthe cutting blades include diamond grains bound on the opening endportion from an inner peripheral side of the core body to an outerperipheral side of the core body.

In accordance with the cutting portion structure constructed asdescribed above, the diamond grains are bound on the opening end portionof the core body in a region from an inner peripheral face of the corebody, through an end face of the opening end portion, and to an outerperipheral face of the core body, and the opening end portion of thecore body is rounded without edges, it is possible to inhibit stressfrom concentrating on specified diamond grains.

For the above reasons, the diamond grains do not disengage from the corebody, and do not locally wear. As a result, the drill bit can carry outdrilling holes in an optimal condition for a long time period, andtherefore can continue to drill a hole having a substantially perfectcircle shape for a long time period.

In addition, since the cutting blades including the diamond grains arearranged with gaps between the cutting blades, the chips generatedduring drilling holes in concrete, stone, etc, can be dischargedsmoothly through the gaps.

In the cutting portion structure of a core drill, the opening endportion may be partially expanded in the radial direction to have athickness larger than a thickness of a base end side portion of the corebody which is closer to a base end of the core body than the opening endportion is, and the expanded portion of the opening end portion may beentirely rounded as viewed from the direction substantiallyperpendicular to a cross-section in the radial direction. In thisconstruction, since it is possible to prevent the base end side portionof the core body from contacting the material in which the hole is beingdrilled, drilling holes is carried out with small cutting reactiveforce.

In addition, since a space is formed between the outer peripheral faceof the core body and an inner peripheral face of the drilled hole, thechips resulting from cutting are discharged smoothly through the space.

As a result, the holes are drilled in concrete, stone, etc in a shorttime and under a small energy condition. Further, after the drilling,the core drill can be easily pulled up from the hole.

The cutting portion structure of a core drill may further comprise astep portion formed between the opening end portion and the base endside portion of the core body. The step portion increases the rigidityof the opening end portion of the core body and makes it possible todrill holes with a substantially perfect circle shape. In addition, thestep portion scrapes up the chips to allow the chips to be dischargedmore efficiently.

The cutting portion structure of a core drill may further comprise agallet formed on a portion of the core body which is located forwardrelative to the cutting blade in a rotational direction of the drill bitsuch that the gallet is located adjacent the cutting blade to allowchips resulting from cutting to be discharged therethrough. The gallet,along with the above mentioned construction cause the chips generated atthe tip end portion of the cutting blade to be smoothly discharged fromthe tip end portion toward the outer peripheral face of the core body.

In the cutting portion structure of a core drill, the gallet may bestructured such that a bottom portion thereof is located radially inwardrelative to an outer peripheral face of the core body, and an upper endportion of the gallet may form a face continuous with a base end sideportion of the core body which is located above the gallet. Thereby thechips can be discharged smoothly.

The cutting portion structure of a core drill, may further comprise aprotruding portion formed in a spiral shape on an outer peripheral faceof the base end side portion of the core body which is located above thegallet to allow chips generated by the cutting blade to be dischargedtoward the base end. With such a cutting portion structure of the coredrill, the chips are discharged efficiently.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional front view showing a construction ofan entire core drill according to an embodiment of the presentinvention;

FIG. 2 is a bottom view showing arrangement of cutting blades includingdiamond grains of the core drill of FIG. 1;

FIG. 3 is a partially enlarged cross-sectional view showing a detailedstructure of the cutting blade;

FIG. 4 is a partial cross-sectional front view showing a construction ofa core drill according to another embodiment of the present invention;

FIG. 5 is a partial cross-sectional view showing a detailed structure ofthe cutting blade including the diamond grain of the core drill shown inFIG. 4;

FIG. 6 is a partial cross-sectional view showing a detailed structure ofa cutting blade having a structure different from that of FIG. 5; and

FIG. 7 is a partial cross-sectional view showing a detailed structure ofa cutting blade having a structure different from those of FIGS. 3 and5.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of a core drill of the present invention willbe described with reference to the drawings.

Embodiment 1

Hereinafter, a core drill according to a first embodiment of the presentinvention will be described with reference to the drawings.

As shown in FIGS. 1 and 2, a core drill A of this embodiment comprises acylindrical core body 1 having an upper end portion with a reduceddiameter and cutting blades 2 provided at an opening end portion 4 ofthe core body 1 and configured to perform cutting. The cutting blades 2are formed at the opening end portion 4 of the core body 1 such thatthey are arranged in a circumferential direction of the core body 1 withpredetermined gaps 3 of a predetermined dimension. As shown in FIG. 3,the cutting blades 2 are formed such that a plurality of diamond grainsare bound in a range from an inner peripheral face 5 of the opening endportion 4, through an end face (opening end face)4A of the opening endportion 4, and to an outer peripheral face 6 of the opening end portion4.

As shown in FIG. 3, in this embodiment, the opening end portion 4 of thecore body 1 is partially expanded in a radial direction of the core body1 to have a thickness larger than that of a base end side portion 1D ofthe core body 1 which is located closer to the base end of the core body1 than the opening end portion 4 is, and its tip end portion 1s roundedin a semispherical shape as viewed from the direction substantiallyperpendicular to the cross-section 1n the radial direction. In addition,step portions 7 are formed between the opening end portion 4 and theinner peripheral face 5 of the base end side portion 1D and between theopening end portion 4 and the outer peripheral face 6 of the base endside portion 1D. The step portions 7 are formed such that the openingend portion 4 is partially expanded radially to increase diameter.

As shown in FIG. 3, the diamond grain is bound to cover a region fromthe inner peripheral face 5 of the base end side portion 1D, through thestep portion 7 on the inner peripheral face 5 side, the end face 4A, andthe step portion 7 on the outer peripheral face 6 side, and to the outerperipheral face 6 of the base end side portion 1D (upper end side inFIG. 3). Therefore, the diamond grain is bound in a semispherical roundshape on the opening end side (lower end side in FIG. 3) to conform toan outer shape (cross-sectional shape) of the opening end portion 4. Inother words, in this embodiment, the cutting blade 2 has a droplet shapeas the cross-section in the radial direction 1s seen from forward in arotational direction.

In an entire construction, as shown in FIG. 2, the cutting blades 2 areformed at the opening end portion 4 which is ring-shaped as seen in abottom view of the core body 1 such that they are arranged with the gaps3 in the circumferential direction as described above. In thisembodiment, in order to enable smooth cutting and discharge of the chipsresulting from cutting, a length of the gaps 3 in the rotationaldirection is set to a length of approximately ½ to ⅓ of the cuttingblade 2. As the length of the gaps 3 increases, vibration and impactincrease during cutting. Conversely, as the length of the gaps 3decreases, discharge of the chips is not smoothly carried out.

A center drill 20 is provided at the center of the core body 1 toposition a rotation center for drilling. In FIG. 2, the center drill isomitted.

When the core drill A constructed as described above is used fordrilling holes in concrete, stone, etc, it functions as described below.Since an outermost end and an innermost end of each cutting blade 2 arelocated radially inward relative to the inner peripheral face 5 of thebase end side portion 1D of the core body 1 and radially outwardrelative to the outer peripheral face 6 of the base end side portion 1D,respectively, and the tip end portion of each cutting blade 2 is formedin a semispherical shape (droplet shape) formed by a continuous facefrom the inner peripheral face 5 to the outer peripheral face 6, acutting reactive force generated by cutting is applied to substantiallyuniformly to the tip end portion of each cutting blade 2. In otherwords, the cutting reactive force does not concentrate on a specifiedregion of the cutting blade 2.

For the above mentioned reason, the diamond grains at the tip endportions of the cutting blades 2 do not partially disengage or wear outafter a long-time use for drilling. As a result, the core drill A showsstable and well-balanced cutting performance. Since the core drill Aperforms cutting smoothly, the life of the core drill A is significantlyimproved.

In contrast to the base end side portion 1D of the core body 1, eachcutting blade 2 is radially partially expanded to increase thickness,the inner peripheral face 5 or the outer peripheral face 6 of the corebody 1 does not substantially contact the material in which the hole isbeing drilled, such as concrete or stone, only a minimum reactive forcerequired for cutting is generated.

The chips resulting from cutting by each cutting blade 2 are smoothlydischarged through the gap 3, through a sufficiently large space formedbetween the outer peripheral face 6 of the core body 1 and the materialsuch as concrete or stone which is located radially outward of the outerperipheral face 6, and then to outside. In addition, since the stepportions 7 scrape up the chips toward the base end of the core body 1,the chips are discharged more efficiently. In particular, when the coredrill A is pulled up from the drilled hole after the cutting, the chipscan be efficiently discharged from the hole.

While in this embodiment, the opening end portion 4 is radially expandedto increase thickness to form the step portions 7 between the openingend portion 4 and the base end side portion 1D of the core body 1, itmay alternatively be configured not to be radially expanded, i.e.,configured to be flat, without substantial step portion 7 as shown inFIG. 6. As a matter of course, the dimension of the step portions 7 maybe reduced. The semispherical shape of the opening end portion 4 may bereplaced by a shape shown in FIG. 6, in which an inner end 4 a and anouter end 4 b of the end face 4A of the opening end portion 4 is roundedwithout edges. Further, while the round inner end 4 a and the roundouter end 4 b are coupled to form a curved line in the cutting portionstructure in FIG. 6, the opening end portion 4 may be structured suchthat a straight-line portion is interposed between rounded portions witha curvature smaller than that of FIG. 6.

Embodiment 2

As a first alternative embodiment (second embodiment) of the firstembodiment, as shown in FIG. 4 or 5, chip discharge gallets 9 are formedat portions of the core body 1 which are located forward of the cuttingblades 2 in the rotational direction and adjacent the cutting blades 2to enable the chips resulting from cutting by the cutting blades 2 to bedischarged toward the base end (upward in FIG. 4) of the core drill A.In this embodiment, the gallet 9 is inclined such that its tip end(lower end in FIG. 4) is located forward in the rotational directionrelative to the base end (upper end in FIG. 4) of the core drill A toenable the chips resulting from cutting by the tip end portion of thecutting blade 2 to be efficiently guided toward the base end.

In such a construction, the chips resulting from cutting by each cuttingblade 2 are discharged through the gallet 9 located forward of thecutting blade 2, through a groove 11 formed on an outer peripheral faceof the core body 1 to extend in a spiral shape, and to outside of thedrilled hole. In FIG. 5, 9 a denotes a bottom face of the gallet 9,which forms a flat face (face) continuous with the outer peripheral face6 of the core body 1.

As shown in FIG. 6, the bottom face 9 a of the gallet 9 may be formed bycutting an outer peripheral face 4 d of the opening end portion 4 of thecore body 1 radially inward (leftward in FIG. 6). Thereby, more chipsare discharged toward the base end. In such a structure, an upper endportion of the gallet 9 is desirably gradually inclined radially outwardso that the upper end portion becomes continuous with the outerperipheral face 6.

As shown in FIG. 1 or FIG. 4, it is preferable that a protruding portion10 is formed on the outer peripheral face 6 of a portion of the corebody 1 which is located above the tip end portion of the cutting blade 2(or gallet 9) to protrude radially outward and to extend in a spiralshape to form a spiral groove 11, in order to efficiently discharge thechips. As a matter of course, the spiral shape is inclined toward thebase end in a rearward region of the core body 1 in the rotationaldirection. In these embodiments, the protruding portion 10 isrectangular in cross-section, but is not intended to be limited to this.Further, two or more spiral grooves may be formed instead of one spiralgroove shown in FIG. 1.

As shown in FIG. 7, as another alternative embodiment, a step portion 7which is similar to that of the embodiment shown in FIGS. 3 and 5 may bedesirably formed between the opening end portion 4 of the core body 1and the inner peripheral face 5 of the base end side portion 1D of thecore body 1 so as to be radially expanded, and the diamond grain maydesirably be bound on only the opening end portion 4 (located lower inFIG. 7) to thereby form the cutting blade 2. When drilling is performedand the core drill A is pulled up from the drilled hole, the exposedstep portion 7 scrapes up the chips toward the base end of the core body1 to a greater degree. In FIG. 7, the same reference numerals as thosein FIG. 5 denote the same or corresponding parts.

INDUSTRIAL APPLICABILITY

The present invention is applicable to drilling of materials to beground, such as concrete, stone, tile, steel, or a composite material ofthese (e.g., concrete covering a surface of steel).

1. A cutting portion structure of a core drill including a cylindricalcore body; and cutting blades, the cutting portion structure comprising:an opening end portion formed on the cylindrical core body, the openingend portion having a tip end portion rounded in a semispherical shape asviewed from a direction substantially perpendicular to a cross-sectionin a radial direction of the core body, wherein the cutting blades areformed at the opening end portion of the cylindrical core body andarranged in a circumferential direction of the core body to have gapsbetween the cutting blades, and the cutting blades include diamondgrains bound on the opening end portion from an inner peripheral side ofthe core body to an outer peripheral side of the core body, wherein theopening end portion is partially expanded in the radial direction tohave a thickness larger than a thickness of a base end side portion ofthe core body which is closer to a base end of the core body than theopening end portion is, and the expanded portion of the opening endportion is entirely rounded as viewed from the direction substantiallyperpendicular to the cross-section in the radial direction, the cuttingportion structure further comprising a step portion formed between theopening end portion and the base end side portion of the core body toform a right angle between the step portion and the base end sideportion.
 2. The cutting portion structure of a core drill according toclaim 1, further comprising: a gallet formed on a portion of a tip endportion of the core body which is located forward relative to thecutting blade in a rotational direction of the core drill such that thegallet is located adjacent the cutting blade to allow chips resultingfrom cutting to be discharged therethrough.
 3. The cutting portionstructure of a core drill according to claim 2, wherein the gallet isstructured such that a bottom portion thereof is located radially inwardrelative to an outer peripheral face of the core body, and an upper endportion of the gallet forms a face continuous with a base end sideportion of the core body which is located above the gallet.
 4. Thecutting portion structure according to claim 3, further comprising: aprotruding portion formed in a spiral shape on an outer peripheral faceof the base end side portion of the core body which is located above thegallet to allow chips generated by the cutting blade to be dischargedtoward the base end.
 5. The cutting portion structure according to claim2, further comprising: a protruding portion formed in a spiral shape onan outer peripheral face of the base end side portion of the core bodywhich is located above the gallet to allow chips generated by thecutting blade to be discharged toward the base end.